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AA Car Care: The science behind your air con

Regular care will keep that cool air coming at the touch of a button. Picture / Getty Images

The temperature's rising, and when it's so hot outside that your icecream melts in seconds, you will at some point be seeking cool relief in your car if you're hitting the road this summer.

Many vehicle interface systems are now designed to set your air conditioning at the press of a button, but what is happening in the background?

How does air con work?

Air conditioning systems are closed circuits, operating in a similar way to how your fridge works, and they contain high and low pressure elements.

The high pressure component forces gaseous refrigerant (coolant) into the condenser with the compressor, which is driven by a belt connected to the engine.

This process heats the compressed refrigerant which is then cooled by the condenser and turned into a liquid under pressure. The low pressure component is what causes all the magic to happen.

The pressurised refrigerant, now a liquid, is forced through the expansion valve and evaporator. In simple terms, the low pressure coolant turns into icy cold gas.

The evaporator is inside the vehicle and the system uses the heater fan to blow air through the chilled unit, forcing the cooled air out of the vents.

How can I help my air con to perform efficiently?

On a hot day, the inside of a vehicle can reach temperatures in excess of 60C which is why you never want to leave children or pets unattended in vehicles.

To help alleviate these temperatures, try to park the vehicle in shaded areas and use a windscreen shade to keep the heat off the dashboard. This will not only keep the dashboard and vents cool, it will stop the steering wheel from getting hot and uncomfortable to hold.

If your vehicle is like a sauna inside after sitting in the sun all day, you can help the air conditioning system by opening all the windows for a few minutes to expel the heat before turning on the air con. Driving with the windows down will also force the hot air out much quicker.

For best cooling results, once you have removed the hot air from the cabin, close all windows and then use the air con in recirculation mode. This will help circulate the already-cooled air; it's more efficient than continuously drawing in warm air from outside.

Does air-con use more fuel than having your windows down?

Driving with the windows down can create wind disturbance which lessens the vehicle's aerodynamics, and means more effort is needed to push the vehicle along.

Air conditioning use puts extra load on the engine while in operation, causing the engine to use more energy and both can contribute in a small way to greater fuel usage.

We'd recommend a balanced compromise. Perhaps wind the windows down at low speeds, and set the air-con for the highway to reduce drag, cabin noise and disturbance.

Why do I have a puddle of water under the car after using the air con?

A good question! The chilled gas passing through the evaporator creates condensation which freezes and melts. It is then drained outside through a hose placed beneath your vehicle.

If this hose is blocked or becomes disconnected, it can result in water leaking on to the floor by your feet.

If you don't see a puddle forming after parking (and using the air con), close inspection may be needed to ensure everything is working as it should be.

Keeping your system operating effectively

Regular cleaning or replacement of the cabin filter (if equipped) will ensure the quality of the air drawn into the cabin is free from leaves, pollen and pollutants that can gradually clog the filter.

Over time, you may notice that the system isn't as cold or effective as it once was. The refrigerant may gradually lose its pressure and it might require a simple top-up, or there may be a fault that has caused the gas to leak.

If this happens, talk to your mechanic to get your air conditioning system checked.

What body type?

What year?

What's your Budget?

Total Price

Per Week

Calculations are based on an interest rate of 10% per annum over a 3 year term with no deposit.
This budget tool is intended as a guide and starting point only and is not in any way a finance quotation. Please refer here for our site terms.

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